1. Field of the Invention
This invention relates to heat exchangers for transferring heat energy between two separate fluids. More particularly, the present invention relates to a wrapped fin heat exchanger having a fin material wrapped about a tube to form an enhanced heat transfer surface. Specifically, the present invention concerns the spacing of the loops of wrapped fin tubing forming a heat exchanger to promote equal heat transfer between fluid flowing through the tubing and heat transfer fluid flowing over the tubing notwithstanding the flow irregularities due to the location of a fan for drawing heat transfer medium over the heat exchanger.
2. Description of the Prior Art
It is known to manufacture a heat transfer surface formed by having a base tubular member fabricated from aluminum or another heat transfer material and having a fin material helically would about the base member. This fin material may be formed in a U-shapes and wrapped about the tube with the base of the fin contacting the exterior surface of the base tube to form a metal to metal contact promoting heat transfer from the tube to the fin. By this extended fin surface, it is possible to provide increased heat transfer between fluid flowing through the tube and a gaseous substance flowing over the tube. The fin surface of the type described is disclosed in U.S. Pat. No. 3,134,166 issued to Venables.
This wrapped fin tubing is specifically formed into a geometrical configuration in conjunction with a heat exchange unit and a fan for circulating air thereover. A heat exchanger of this material has many applications including that of a refrigeration circuit for an air conditioning system wherein refrigerant flows through the tube and air flows over the exterior enhanced portion of the heat exchanger. In this application, heat energy is transferred between air flowing over the exterior and in contact with the wrapped fins of the heat exchanger and a refrigerant flowing through the interior of the tube. A heat exchanger may be formed in many configurations to provide the appropriate air flow relationship thereover. A fan is typically mounted as part of the air conditioning unit for drawing air through or pushing air over the heat transfer surface.
One of the many heat exchanger configurations possible for use in a heat exchange unit is forming the heat exchanger in a cylindrical shape. A long continuous tube may be wrapped into a generally cylindrical configuration to serve as the heat exchanger. This heat exchanger is often mounted in a heat exchange unit including a base pan for supporting the cylindrical heat exchanger and a top cover. A louvered exterior casing for allowing air to flow into and across the heat exchange surfaces is additionally provided. Conventionally, a fan is mounted at the top of the heat exchanger to draw air in through the cylindrical sides of the heat exchanger and to exhaust that air upwardly away from the air conditioning unit. It has been found that when a fan is mounted adjacent one end of a cylindrical heat exchanger for drawing air from the heat exchanger that the air flow through the heat exchanger is uneven. Typically, larger air volume per unit length of heat exchanger are drawn inwardly through the top portions of the heat exchanger adjacent the fan than from the bottom portions of the heat exchanger furthest from the fan. Uneven air flow results in a lessened heat exchanger performance since a reduced air flow passes through a portion of the heat exchanger.
In order to provide for increased heat transfer efficiency for the entire heat exchanger several modifications to the cylindrical configuration of the heat exchanger have been found and are believed to be effective. One manner of providing a more even air flow across the length of the heat exchanger is to space the individual loops of tubing forming the heat exchanger differently. If the loops are spaced more closely together in the higher flow regions the air flow resistance is increased and more air is drawn in through the lower flow regions at the other end of the heat exchanger to balance heat transfer. Additionally, if the tube spacing is closer at the higher flow areas then the given volume flow per loop may be equalized, although the volume flow per unit length is not equalized. It is the volume of air flow per loop which needs to be equalized to promote even heat transfer across the length of the heat exchanger.
Several alternative constructions are disclosed herein for accomplishing the spacing differential to provide for even heat transfer per loop in the heat exchanger. One of these embodiments incorporates a single row heat exchanger having various loops spaced differently along the length thereof. Other embodiments include multiple row heat exchangers wherein a single row is spaced evenly and the second row is spaced according to the air flow patterns or a heat exchanger having multiple rows where the second row extends only over the higher volume flow portion of the heat exchange surface.